1. Field of the Invention
The present invention relates to a semiconductor laser device, an astigmatic correction plate used therefor and a method of arranging the astigmatic correction plate.
2. Description of the Related Art
A typical semiconductor laser has a large number of characteristics, such as compact size, high efficiency, capability of low voltage operation, low power consumption, long life span, capability of high speed modulation and so on, so it is applicable as a light source for optical electronics, such as for optical communications or for reading data from an optical storage medium in various fields. Such a semiconductor laser device emits one kind of a laser beam from one element; however, as a derivative of the device, two-wavelength semiconductor laser devices emitting two kinds of laser beams with different wavelengths from one element have been proposed in, for example, Japanese Unexamined Patent Application Publication No. Hei 10-302289, Japanese Unexamined Patent Application Publication No. Hei 09-283853, Japanese Unexamined Patent Application Publication No. Hei 02-253676, Japanese Unexamined Patent Application Publication No. Sho 56-80195, Japanese Unexamined Patent Application Publication No. Sho 60-164381, Japanese Patent Publication No. 3095036, Japanese Patent Publication No. 3197050 and so on, and some of them are already in practical use.
FIG. 1 shows an example of such conventional two-wavelength semiconductor laser device. In the conventional two-wavelength semiconductor laser device, on a laser diode chip 16 with, for example, a double heterojunction structure, a first laser light source 11 of a light emitting point which emits a laser beam with a predetermined wavelength is arranged, and a second laser light source 12 which emits a laser beam with a different wavelength from that of the laser beam emitted from the first laser light source 11 is arranged at a predetermined distance from the first laser light source 11. In order to correct the astigmatism of the laser beams emitted from the first laser light source 11 and the second laser light source 12, an astigmatic correction plate 13 is arranged so as to intersect diagonally the optical axes of the laser beams.
The astigmatic correction plate 13 is arranged on a backside of a top surface of a so-called slanted cap 18 having an aperture with a predetermined effective diameter. The slanted cap 18 is arranged so as to cover the laser diode chip 16, and thereby a main surface of the astigmatic correction plate 13 intersects diagonally optical axes 15 and 19 of the laser beams emitted from the laser diode chip 16.
In such two-wavelength semiconductor laser device, as shown in FIG. 2, the astigmatic correction plate 13 is arranged in a slanting position, so the optical axes 15 and 19 of the laser beams are shifted due to refraction in the astigmatic correction plate 13. Therefore, the first laser light source 11 is arranged in a position shifted from a center line (CL) of the effective diameter of the aperture on purpose.
On the other hand, in much the way that the position of the first laser light source 11 is shifted, the second laser light source 12 is arranged in a position shifted by a predetermined distance from the first laser light source 11 to a direction in which a distance to the main surface of the astigmatic correction plate 13 becomes longer.
However, in the above, conventional two-wavelength semiconductor laser device, as schematically shown in FIG. 3, there is a problem that, specifically, an emission angle (a region capable of emission) of the laser beam emitted from the second laser light source 12 becomes extremely narrow.
In view of the foregoing, it is an object of the present invention to provide a semiconductor device capable of increasing an emission angle of a laser beam, an astigmatic correction plate used therefor and a method of arranging the astigmatic correction plate.
A semiconductor laser device emitting two wavelengths different from each other according to the invention comprises: a first laser light source emitting a laser beam with a first wavelength; a second laser light source arranged at a predetermined distance from the first laser light source emitting a laser beam with a second wavelength; and an astigmatic correction plate comprising a light transmitting plate with a predetermined thickness, the astigmatic correction plate being arranged so as to intersect diagonally an optical center line or an optical axis of at least one of the laser beams emitted from the first laser light source and the second laser light source in order to correct the astigmatism of the laser beam, and emitting the laser beam from an aperture with a predetermined effective diameter to outside, wherein the first laser light source and the second laser light source are arranged on both sides of a center line of the effective diameter so as to have different distances to the astigmatic correction plate in a direction parallel to the optical center line or the optical axis.
Another semiconductor laser device emitting two wavelengths different from each other according to the invention comprises: a first laser light source emitting a laser beam with a first wavelength; a second laser light source arranged at a predetermined distance from the first laser light source emitting a laser beam with a second wavelength; and an astigmatic correction plate comprising a light transmitting plate with a predetermined thickness, the astigmatic correction plate being arranged so as to intersect diagonally an optical center line or an optical axis of at least one of the laser beams emitted from the first laser light source and the second laser light source in order to correct the astigmatism of the laser beam, and emitting the laser beam from an aperture with a predetermined effective diameter to outside, wherein the first laser light source is arranged in such a position that an optical center line or an optical axis of the first laser light source almost coincides with a center line of the effective diameter of the astigmatic correction plate, and the second laser light source is arranged so that a distance from the second laser light source to the astigmatic correction plate in a direction parallel to the optical center line or the optical axis is shorter than a distance from the first laser light source to the astigmatic correction plate.
In an astigmatic correction plate used for a semiconductor laser device according to the invention, the semiconductor laser device comprises a first laser light source emitting a laser beam with a first wavelength and a second laser light source arranged at a predetermined distance from the first laser light source emitting a laser beam with a second wavelength, and the astigmatic correction plate, which is arranged so as to intersect diagonally an optical center line or an optical axis of at least one of the laser beams emitted from the first laser light source and the second laser light source in order to correct the astigmatism of the laser beam, and which emits the laser beam from an aperture with a predetermined effective diameter to outside, comprises a light transmitting plate body with a predetermined thickness, wherein the astigmatic correction plate is arranged so that the first laser light source and the second laser light source have different distances to the astigmatic correction plate in a direction parallel to the optical center line or the optical axis, and the first laser light source and the second laser light source are arranged on both sides of a center line of the effective diameter.
In another astigmatic correction plate used for a semiconductor laser device according to the invention, the semiconductor laser device comprises a first laser light source emitting a laser beam with a first wavelength and a second laser light source arranged at a predetermined distance from the first laser light source emitting a laser beam with a second wavelength, and the astigmatic correction plate, which is arranged so as to intersect diagonally an optical center line or an optical axis of at least one of the laser beams emitted from the first laser light source and the second laser light source in order to correct the astigmatism of the laser beam, and which emits the laser beam from an aperture with a predetermined effective diameter to outside, comprises a light transmitting plate body with a predetermined thickness, wherein the astigmatic correction plate is arranged so that an optical center line or an optical axis of the first laser light source almost coincides with a center line of the effective diameter and a distance from the second laser light source to the astigmatic correction plate in a direction parallel to the optical center line or the optical axis is shorter than a distance from the first laser light source to the astigmatic correction plate.
In a method of arranging an astigmatic correction plate according to the invention, the astigmatic correction plate is used for a semiconductor laser device comprising a first laser light source emitting a laser beam with a first wavelength and a second laser light source arranged at a predetermined distance from the first laser light source emitting a laser beam with a second wavelength, and the astigmatic correction plate, which is arranged so as to intersect diagonally an optical center line or an optical axis of at least one of the laser beams emitted from the first laser light source and the second laser light source in order to correct the astigmatism of the laser beam, and which emits the laser beam from an aperture with a predetermined effective diameter to outside, comprises a light transmitting plate body with a predetermined thickness, and the method comprises the step of arranging the astigmatic correction plate so that the first laser light source and the second laser light source have different distances to the astigmatic correction plate in a direction parallel to the optical center line or the optical axis and the first laser light source and the second laser light source are arranged on both sides of a center line of the effective diameter.
In another method of arranging an astigmatic correction plate according to the invention, the astigmatic correction plate is used for a semiconductor laser device comprising a first laser light source emitting a laser beam with a first wavelength and a second laser light source arranged at a predetermined distance from the first laser light source emitting a laser beam with a second wavelength, and the astigmatic correction plate, which is arranged so as to intersect diagonally an optical center line or an optical axis of at least one of the laser beams emitted from the first laser light source and the second laser light source in order to correct the astigmatism of the laser beam, and which emits the laser beam from an aperture with a predetermined effective diameter to outside, comprises a light transmitting plate body with a predetermined thickness, and the method comprises the step of arranging the astigmatic correction plate so that an optical center line or an optical axis of the first laser light source almost coincides with a center line of the effective diameter and a distance from the second laser light source to the astigmatic correction plate in a direction parallel to the optical center line or the optical axis is shorter than a distance from the first laser light source to the astigmatic correction plate.
According to the semiconductor laser device, the astigmatic correction plate used therefor and the method of arranging the astigmatic correction plate of an aspect of the invention, the astigmatic correction plate comprising a light transmitting plate body with a predetermined thickness is arranged so as to intersect diagonally an optical center line or an optical axis of at least one of the laser beams emitted from the first laser light source and the second laser light source in order to correct the astigmatism of the laser beam, and the astigmatic correction plate emits the laser beam from an aperture with a predetermined effective diameter to outside. Further, the astigmatic correction plate is arranged so that the first laser light source and the second laser light source have different distances to the astigmatic correction plate in a direction parallel to the optical center line or the optical axis, and the first laser light source and the second laser light source are arranged on both sides of a center line of the effective diameter. Thereby, an incident angle of the laser beam emitted from the first laser light source and an incident angle of the laser beam emitted from the second laser light source to the astigmatic correction plate can become wider than ever.
According to the semiconductor laser device, the astigmatic correction plate used therefor and the method of arranging the astigmatic correction plate of another aspect of the invention, in the method of arranging the astigmatic correction plate used for the semiconductor laser device comprising a first laser light source emitting a laser beam with a first wavelength and a second laser light source arranged at a predetermined distance from the first laser light source emitting a laser beam with a second wavelength, the astigmatic correction plate comprising a light transmitting plate body with a predetermined thickness is arranged so as to intersect diagonally an optical center line or an optical axis of at least one of the laser beams emitted from the first laser light source and the second laser light source in order to correct the astigmatism of the laser beam, and the astigmatic correction plate emits the laser beam from an aperture with a predetermined effective diameter to outside. Further, the astigmatic correction plate, the first laser light source and the second laser light source are arranged so that an optical center line or an optical axis of the first laser light source almost coincides with a center line of the effective diameter and a distance from the second laser light source to the astigmatic correction plate in a direction parallel to the optical center line or the optical axis is shorter than a distance from the first laser light source to the astigmatic correction plate. Thereby, not only an incident angle of the first laser beam emitted from the first laser light source to the astigmatic correction plate but also, specifically, an incident angle of the second laser beam emitted from the second laser light source to the astigmatic correction plate can become wider than ever.
Other and further objects, features and advantages of the invention will appear more fully from the following description.